What comes out of the brush to sit on the sand?

Short Answer: Rabbits come out of the brush to sit on the sand by the Salinas River.
In the opening paragraph of Steinbeck's classic novella, he describes the tranquil riverbank, where trees arch over the glistening Salinas River and the rocky Gabilan Mountains stand out in the background. Steinbeck then writes that in the evening, lizards run over crisp leaves and rabbits come out of the brush to sit on the sand.
Before George and Lennie travel down the worn path to the riverbank, the atmosphere is completely still, and Steinbeck describes the rabbits sitting on the sand as little gray sculptured stones. Throughout the novel, Lennie is infatuated with rabbits because of his affinity for petting soft things. Lennie continually fantasizes about tending rabbits on a private homestead with George and makes George repeat their fantasy as a brief respite from their difficult lives.